Caustic-soda process.



UNITEDTSTATES PATENT OFFICE.

JULES HECTOR HIRT, OF EL PASO, TEXAS.

CAUSTIC-SOIDA PROCESS.

Specification of Letters Patent.

Patented Sept. '7, 1915.

1,152,949. Ho Drawing. Application filed February 11, 1913. Serial No. 747,607.

To all whom it may concern Be it known that 1, Jonas HECTOR Him, a citizen of the United States, residing at El Paso, in the county of El Paso and State of Texas, have invented certain new and useful Improvements in Caustic-Soda Processes, of which the following is a specification.

This invention relates to a caustic-soda process and product, and its object is to produce caustic soda (2NaOl-l) at low cost.

In carrying out m new Process, I take approximately anhy rous sodium-sulfate (Na SO and mix it with about one-half its weight of saw-dust, either wet or dry, and charge the hot end (near the fire bridge) of a reverberatory tank-furnace, preferably continuously, with the mixture.

Under the furnace heat, the sodium sulfate melts at a temperature of 880 C. and immediately begins to be reduced by destructive distillation of the saw-dust, to sodium sulfid, in consequence of the combined action of volatile, heavy hydrocarbons in the saw-dust and of the extremely porous charcoal into which the saw-dust is converted by the destructive distillation of it.

The sodium sulfid produced, fuses at a temperature of about600 0., and in consequence the bath of sodium sulfid is extremely mobile, having a consistency about that of milk. In this freely fluid state it can be readily tapped from the furnace tank at the cool end. This freely-flowing sodiumsulfid product of the furnace is partially protected from oxidation in air by the soot which is disseminated through the bath, the soot resulting from the destructive distillation of the saw-dust. And while in the furnace, the saw-dust floats on top of the sodium-sulfid bath and there protects the bath from oxidizing action by the flame.

An advantage of using the saw-dust is that the hydrocarbons released in the dc.- structive distillation of the saw-dust effect a very rapid reduction of the sodium sulfate to sodium sulfid and produce most of the soot which protects the molten sulfid from oxidation. The importance of protecting the molten sulfid from oxidation is that a if it be not so protected when tapped out in its liquid form from the furnace, it will burst spontaneously into flame and thereby will revert, or will tend to revert, back into sodium sulfate.

The saw-dust floating on the bath constitutes a covering of more or less depth, and which is exposed directly to the reverberatory-furnace flame and heat. The temperature of the bath is necessarily higher than the temperature of the saw-dust, and the bath boils up through the saw-dust covering while the saw-dust is undergoing the destructive distillation, so that the oxidationresisting soot is well distributed throughout the molten sulfid.

4 As saw-dust contains only about onethird of one per cent. of ash, its use results m a purer product than would be obtained if coal or coke, which contain about ten per cent. of ash, were used in lieu of the sawdust.

In the production of caustic soda (QNaOH), or sodium hydrate, the sodium sulfid in its freely fluid state is tapped from the furnace into, and is cooled in, water contained in vats and in which water the sodium sulfid is soluble.

In the vat or vats, hot or cold milk of lime or calcuim hydrate (CaOH,) in dilute solution is added, and the liquor in each suceesslve vat becomes more and more caustic, the sodium sulfid becoming converted into caustic soda in accordance with the formula The calcium sulfid is insoluble in .water in the presence of calcium hydrate, and precipitates.

While hot milk of lime can be added to an aqueous solution of sodium sulfid in excess of the quantity which is required to effect the reaction, yet only a portion of the sodium sulfid will in that case be converted into sodium hydrate or caustic soda for in the vats the particles of calcium hydrate become coated with insoluble calcium sulfid, and such coating interferes with the conversion of the sodium sulfid into sodium hydrate. Thus if milk of lime were added to any vat in large excess, or otherwise than in diluted solution, the reaction would be in accordance with the above formula, but incomplete.

Under the foregoin condition only a small portion of the so ium sulfid would be converted into caustic soda. hand, by adding the milk of lime to the contents of the vat or vats in successive small portions, the reaction proceeds with rapidity and completeness in the production of On the other 2. The process of making caustic sod messes consisting in flowing molten sulfid of sodium into water and thereby dissolving the sulfid and in adding to the hot solution, calcium hydrate.

In testimony whereof I aflix my signature 1:,

in presence of two witnesses.

JULES HECTOR HIRT. Witnesses:

G. BLAKE, EDWARD E. Bmox. 

